Spinning solvent for acrylic fibers



United States Patent 2,776,945 SPINNING SOLVENT FOR ACRYLIC FIBERSForrest I. Ralll, Morristown, and Harry H. Weinstock,

Jr., Madison, N. J., assignors to Allied Chemical & Dye

gorporation, New York, N. Y., a corporation of New No Drawing.Application July 22, 1954, Serial No. 445,156

Claims. (Cl. 260-32.6)

This invention relates to spinning solutions 4for production ofiilaments from copolymers of acrylonitrile and at least one othersubstance having ethylen-ic saturation, and more particularly to suchspinning solutions wherein the copolymers contain at least 70 weightpercent acrylonitrile.

Extruded fibers from copolymers having high (70 weight percent or more)acrylonitrile content are particularly valuable for making a diversityof textiles. However, a high proportion of acrylonitrile generallyrenders the copolymer incapable of solution in ordinary solvents forconventional spinning methods.

lt has been proposed therefore to incorporate into copolymers of highacrylonitrile content monomers having groups such as hydroxyl radicalswhich will enhance the solubility of the copolymer in common solvents.Thus the copolymers are restricted to certain highly specific types oflimited usefulness, and to produce them it is necessary to use monomericmaterials which may be -dif'- cult or very costly to obtain.

It has been proposed also to employ N,Ndimethyl formamide, N,Ndimethylacetamide, nitromethane, and mixtures of nitromethane with formamide toobtain spinnable solutions of the copolymers. r

Among the deficiencies of such solvent mediums for making spinningsolutions are, in some cases, their low miscibility with water for rapidsolvent removal in aqueons co-agulating baths; in other cases, their lowvolatility necessitating high temperatures for solvent removal if dry`spinning processes are attempted; their high cost; the instability ofthe spinning solutions made up with them which lead to gel formation ifnot used promptly after making up; and their inability to make spinningsolutions, which have viscosity in the range of 1,000" to. 30,000

centiposes for moderate power consumption together with a Isolidscontent of atleast 10 and: particularlyI of 15 or more, weight, percentcopolymer.

An object ot this invention is an improved spinning solvent for use inthe production ofy filaments. from copolymers of acrylonitrile with atleast one. other substancehaving ethylenic unsaturation, said copolymerscontaining at least 7-0 weight percent acryl'onitrile, and particularlyfrom copolymers of this type which are diicultly soluble.

Another object of.V this invention is spinning solutionsv for productionof filaments from. copolymersA of the type: described', which;ysolutions are characterized by their high solids content coupled withmoderate spinning viscosity, their stability, their clarity, and theirability to form; high quality fibers at moderate spinning: solutiontemperatures, e. g, 10P-20. C., at whichV no discoloration: o1'A weak.-`@ning of the liber product occurs.

Still another object of this invention is an improved process for theproduction of lila-mentsfrom the; copolyrners of the typev described.

We,y have now discovered a solventv for; acrylonit-rile copolymers whichhas, unexpected utility in. the7 manufacture of yfilaments therefromand` which. overcomesA C.. gavea. 0.lL% by weight solution.

ICC

many of the objectionable features inherent in previous spinningsolvents. The spinning solvent of our invention consists essentially of5,0 to parts by weight acetonitrile and 50 to 5 parts by weight of, atleast one unsubstituted Ci-Cz saturated aliphatic a'mide. The spinningsolution of our invention consists essentially of a solution in theaforementioned solvent, of a copolymer of acrylonitrile with at leastone other substance having ethylenic unsaturation, said copolymercontaining at least 70 weight percent acrylonitrile.

Our process'comprises dissolving the subject copolymers at a temperatureabove 50 C. in a solvent consisting essentially of 50 to 95A parts byweight acetoni'trile and 50 to 5 parts by weight of an unsubstitu'te'dC21-Cz saturated aliphatic amide, and extruding said solution throughy aspinneret into 'a zone containing a solvent-removing medium.

YBy the term unsubstituted CiCz saturated aliphatic amide wemeanfformamide and acetamide, These amides boil under atmosphericpressures at temperature between 210 and 222 C. Because of the ease withwhich they dissolve the less soluble copolymers, we prefer to use thesolvent mixtures comprising essentially 70 to 90 parts by weightacetonitrle and 30 to l0 parts by weight of the amide. The efficiency ofthe amide in the prac'- tice of our invention decreases as its molecularweight increases. We prefer, therefore, formamide to acetamide.

For simplicity, economy of solvent recovery and eiciency in spinning yatlow temperatures the binary mixtures of acetonitrile and anunsubstituted Ci-Cz saturated aliphatic amide are preferred; It ispossible, however, to dilute the mixulre of essential components withsmall amounts, i. e. l-lS weight percent, of extraneous material such asmethyl acetate, water, etc.; and to mix dyes, stabilizers, ete. into thesolution for spinning. Large amounts of these extraneous materia-lsvshould not be included in our composition since they tend to lower thedissolving elflcieney ofthe solvent.

They acetonitrile and amide components of our copolymer solvent arebothy readily soluble in water which makes for rapid coagulation of theber in a wet spinning process. Suitable iiber can. be spun into watercontaining little or. no solvent; the' speed of coagulation can bereduced if desired by incorporating upV to about 1.045% by weight ofacetonitrile and/or the amide in the aqueous bath. f

The acrylonitrile copolymers of special interest for use in ourinvention are those negligibly soluble in v acetonitrile alone or inCif-Ca. saturated aliphatic amide alone; e. g. extracted. withacetonitri-le at about 82 C. for 16- hours, the copolymer formed from 90parts by weight acrylonitrile monomer and- 10 parts by weight of methylacrylatemonotner and having reduced viscosity ofv about 1.2 gave a 0.35%by weightA solution; and heating a similar copolymer with formamide fortwo hours at Reduced viscosity (R. V.) isA a measure. of averagemolecular weight.- of the copolymer determined by flow from an Ostwal'dpipette and is computed by the4 equation: R. V.='(time' of eliiuic oisolution-time of. eiiiuar o'f solvent)l/ (concentration of copolymer ingrams per 100I cc. of solventXtime: ot eiiiunv ofv solvent); The' valuespresented herein-.were determined aft 40@ C. in! dimethyl forman-lido'solution using.0;1f25 gram: of copolymer per` 1'00 cc".- 6E solvent. Thesolvent of our invention is practical for making, spinning dopesf ofaciyloniftri-le' copolymers containing-,up to-A about 98% acrylonitrile.DopesV containing/substantial amounts of polyacrylonitrile itselfvrequire any impracticallyhigh spinning temperature to stay clear-1solution;4 hence are; bei avfoidedt- 'Iiypioalf acnylonitnile;copolymers which we have found useful in practicing our invention aretabulated below. The acrylonitrile content ofuthese copolymers is atleast 70% by weight (copolymer compositions are expressed in parts byweight of starting monomer).

Because of its dyeability and other valuable fiber properties We preferto use copolymers having weight composition close to 90 partsacrylonitrile and l0 parts methyl acrylate.

For effective lament formation and moderate power consumption thespinning viscosity of the solutions, measured at 73-75 C., should bebroadly in the range of 1,000 to 50,000 centipoises, preferably between3,000 and 15,000 centipoises. To obtain spinning viscosity in the latterrange, the solids content of the solution generally will be in the rangel5-25'weight percent. Solutions having or more weight percent solids aregenerally suitable for spinning. Spinnable solutions can be made havingas much as about 30% solids with many of the copolymers in the solventof our invention.

Rate of solution and completeness of solution increase with temperature.Other factors affecting the rate of solution are `the particularcopolymer and solvent composition and the final solids concentrationdesired. The minimum practical dissolving temperature in the practice ofour invention is at least50 C.; for economy and eciency in our processwe prefer to use dissolving temperatures from about 60 to 110 C. andatmospheric pressure. It is sometimes advantageous to dissolve thecopolymer in a sealed system where temperatures above the atmosphericboiling point of the binary solvent can be used. After solution iscompleted, the solution temperature can be reduced to 70-80 C. forspinning without gel formation.

Deaeration of the spinning solutions of our invention can beaccomplished simply and effectively at atmospheric pressure bymaintaining i the solution between about 50 and 75 C., thus suchoperation is preferred. If the solution temperature is allowed to fallbelow 50 C. some gel formation is likely to occur and cause plugging ofthe spinnerct should care be not taken to completely redissolve the gelbefore spinning, e. g. by warm ing to a temperature above 50 C. In thedeaerating at atmospheric pressure and temperature above 75 C. solventvapor losses can be appreciable and somewhat variable depending upon theamount of air presentand the temperature used. It is possible, ofcourse, to use higher temperatures when deaerating at temperature above75 C., venting against a slight back pressure for conserving solventrather than exposing the dope to atmospheric pressure and allowingexcessive amounts of solvent components to vaporize. Deaerating againstpressure, however, is less eicient than is the preferred atmosphericpressure deaeration at temperatures between about 50 and 75 C. Inrespect to maintaining deaeration of the spinning solution whennon-condensable gases such as nitrogen are used to transfer the solutionto the spinning operation, high gas pressure, i. e. above about l5pounds per square inch gauge, should be avoided to prevent substantialamounts of gas from redissolving in the solution. Gas bubbles in theextruded solution give imperfect yarn formation and filament breakage.

The stability of the spinning solutions of our invention is marked.Retention of the solutions for as long` as 24 hours at spinningtemperatures has no effect on them. This excellent stability permitsquite elastic scheduling in the manufacture of filaments, and it enablesreduction of investment in standby equipment needed to prevent rawmaterial loss andreprocessing when down time due to accident orequipment failures occurs in the plant.

Our solvent permits usefof moderate spinning temperatures, e. g. 70-80C. In spinning we prefer to use a spinning solution temperature of about70-72 C. for maintaining easy extrusion of the solution without thedanger of solvent vapor bubble formation. When dry spinning, solventremoval can be accomplished by use of hot air between about 140-200 C.When wet spinning, solvent removal can be accomplished by extrusion ofsolution into an aqueous coagulating bath maintained about 70 C.Spinning behavior is easily reproducible, and minor temperature changesdo not affect it since the operation can be carried out at a temperaturebelow that which will impart undesirable color to the yarn, yet farabove that at which gel formation is likely to occur. It is possible tomake very light colored yarn using the spinning solutions of ourinvention. Even while the yarn is still wet with solvent during thespinning the strength of the yarn is high. This makes possible fast andeasy handling with few filament breaks.

In a wet spinning process it is often of value to wash the yarn withwater after it has been coagulated in the aqueous bath. This is aneffective way forremoving residual solvent clinging to the fibers. Onesimple and effective yarn-washing procedure involves countercurrentlyrinsing the yarn as it is drawn from the bath, with water over a trough.The rinse water can then be drained into the bath as makeup thereforwhile the solvent-enriched bath water overflows by displacement and issubjected to solvent recovery treatment hereinafter described.

The acetonitrile component can be recovered from an aqueous coagulatingliquid by azeotropic distillation and the amide component as a residualmaterial from the distillation. In a dry spinning process solvent vaporscan be recovered from the air stream by methods such as adsorption onactivated charcoal or low temperature condensation.

The following examples show several ways in which our invention has beencarried out but are not to be construed as limiting it. All partsexpressed are parts by weight, and all solvent composition percentagesare weight percentages.

Example 1.-Copolymer having reduced viscosity of 1.05 was prepared bypolymerizing for four hours in an agitated kettle 10 parts methylacrylate and 90 parts acrylonitrile at a temperature of 35 C. using 1000parts of aqueous medium and as catalyst 3.2 parts of ammonium persulfateand 1.6 parts of sodium metabisultite. Copolymer was then separated,dried, and ground. Yield of copolymer was 88.2% of the weight ofmonomers charged. This copolymer contained more than 70% by weightacrylonitrile, and probably had composition of about 89.2% acrylonitrilewith balance of methyl acrylate as estimated from the proportions ofmonomers used, the yield, and the relative reactivity ratios of themonomers as given in Copolymerization, Alfrey, Bohrer, and Mark, volumeVIII, table 1V, page 91 (Interscience Publishers Inc., New York, N. Y.,1952).

25 parts of the dried and ground copolymer were dissolved in a closedcontainer in a solvent consisting of 52.5 parts of acetonitrile and 22.5parts of formamide using a nitrogen gas blanket and mechanical agitationat a temperature of C.

A clear solution having viscosity of 15,000 cenlipoises at 80 C. wasobtained. The solution was then extruded through a spinnerct which hadl0 holes each 0.005" in diameter, the spinnerct being immersed in anaqueous coagulating bath` maintained at 7273 C. Filamcnts were passedthrough the bath for 20 inches, snubbed around feed rolls, and ledthrough a 36inch aqueous stretching bath maintained at 92-94 C. The yarnwas stretched 2-4 times its initial extruded length by being taken up ona winding device rotating faster than the feed rolls. Filaments werevery light colored and possessed tenacity of 2.02 grams per denier atbreak, said filaments being 4.7 denier/lament. Ultimate elongation ofthe yarn so made was 7.8 percent.

ln place of the aqueous coagulating bath used in the above example, itis possible to remove solvent from the extruded laments by drawing theminto an externallyheated spinning column through which a flow of hot airat 140-200 C. is passed.

Example 2.-Copolymer having reduced viscosity of 2.13 was prepared bypolymerizing for 41/2 hours in an agitated kettle parts methyl acrylateand 90 parts acrylonitrile at a temperature of 35*7 C. using 1400 partsof aqueous medium and asl catalyst 2.8 parts of ammonium persulfate and1.4 parts of sodium metabisulite. Copolynner was then separated, dried,and ground. Yield of copolymer was 71% of the weight of monomerscharged. This copolymer contained more than 70% by weight acrylonitrile,and probably had composition of about 88% acrylonitrile with balance ofmethyl acrylate as estimated from the proportions of monomers used, theyield, and the relative reactivity ratios of the monomers as given inCopolymerization, Alfrey, Bohrer, and Mark, volume VIII, table lV, page91 (Interscience Publishers Inc., New York, N. Y., 1952).

14 parts of the dried and ground copolymer were dissolved in a closedcontainer in a solvent consisting of 68.8 parts of acetonitrile and 12.9parts of formamide and 4.3 parts of H2O using a nitrogen gas blanket andmechanical agitation at a temperature of 94 C. in a closed container.

A clear solution having viscosity of 10,000 to 12,000 centipoises at 75C. was obtained. The solution was then extruded through a spinneretwhich had 40 holes each 0.005 in diameter, the spinneret being immersedin an aqueous coagulated bath maintained at 74 C. Filaments were passedthrough the bath for 24 inches, snubbed around feed rolls, and ledthrough a 36-inch hot air stretching oven at 165 C. The yarn wasstretched 7 times its initial extruded length by being taken up on awinding device rotating faster than the feed rolls. Filaments were verylight colored and possessed tenacity of 2.91 grams per denier at break,said filaments being 2.13 deuier/lament. Ultimate elongation of the yarnso made was 6.5 percent.

Example 3.-The following is a tabular summary of representativecopolymer solutions which have been made up with the solvent of ourinvention. Copolymer cornpositions are identified by the ratios of theirstarting monomers expressed in parts by weight. All the resultingcopolymers contained at least 70% by weight of acrylonitrile.

Weight Dissolvng Copolymer Ratio Percent Solvent Component Tempera-Solids Weight Ratio ture, C.

Methyl aerylate/acryloni- 10 acetonltrile/forma- 60 trlle, 10/90. mideat 90/10.

22 82 15 60-115 15 60-115 Do 15 60-115 Mtarllyl2 9aorylate/aerylonl 20110 e Methy'fiacrynte/vmyndene 15 same at zzo/2o sooll/idgeacrylonitrile. Vinyl acetate/vinylidene 17 acetonitrile/forma-75-78 ghloride/acrylonitrlle, gig/water, Methyl acrylate/acryloni- 15same at 0/15/5--.. 94

trlle, 10/90.

D acetonitrile/forma- 70 m e 20 acetonitrile/aceta- 100 mide,

We claim:

1. A spinning solution consisting essentially of a copolymer ofacrylonitrile and at least one other substance having ethylenicunsaturation, said copolymer containing at least 70 weight percentacrylonitrile, and a solvent for said copolymer consisting essentiallyof 50 to 95 parts by weight acetonitrile and 50 to 5 parts by Weight ofan unsubstituted Ci-Cz saturated aliphatic amide.

2. The spinning solution as defined in claim 1 wherein the reducedviscosity of the copolymer is between 0.7 and 3.0 and solids content isat least 10% by weight.

3. The spinning solution as defined in claim l wherein the reducedviscosity of the copolymer is between 1.0 and 2.3 and solids content isat least about 15% by weight.

4. The spinning solution defined in claim 3 wherein spinning viscosityat 73 C. is in the range of 3,000 to 15,000 centipoises.

5. The spinning solution as defined in claim 4 wherein said amide isformamide.

6. The spinning solution as defined in claim 4 wherein said amide isacetamide.

7. A spinning solution consisting essentially of a polymer ofacrylonitrile and at least one other substance having ethylenicunsaturation, said copolymer being negligibly soluble in acetonitrilealone and formamide alone and containing at least 70 parts by weightacrylonitrile, and a solvent for said copolymer consisting essentiallyof 70 to 95 parts by weight acetonitrile and 30 to 5 parts by weight ofan unsubstituted Ci-Cz saturated aliphatic amide.

8. The spinning solution as defined in claim 7 wherein the copolymercomposition is about parts by Weight acrylonitrile and about 10 parts byWeight methyl acrylate, the reduced viscosity of said copolymer is from1.0 to 2.3, the solvent consists essentially of acetonitrile andformamide, and the solids content is at least about 15 by weight.

9. The spinning solution defined in claim 1 wherein said copolymer ofacrylonitrile s a copolymer with methyl acrylate as one ingredientthereof.

10. The spinning solution dened in claim 7 wherein said copolymer ofacrylonitrile is a copolymer with methyl acrylate as one ingredientthereof.

References Cited in the le of this patent UNITED STATES PATENTS

1. A SPINNIG SOLUTION CONSISTING ESSENTIALLY OF A COPOLYMER OFACRYLONITRILE AND AT LEAST ONE OTHER SUBSTANCE HAVING ETHYLENICUNSATURATION, SAID COPOLYMER CONTAINING AT LEAST 70 WEIGHT PERCENTACRYLONITRILE, AND A SOLVENT FOR SAID COPOLYMER CONSISTING ESSENTIALLYOF 50 TO 95 PARTS BY WEIGHT ACETONITRILE AND 50 TO 5 PARTS BY WEIGHT OFAN UNSUBSTITUTED C1-C2 SATURATED ALIPHATIC AMIDE.